Abstract: In this paper, the impedance matching problem in high speed driving laser diodes is dealt with and tapered transmission lines are introduced as an impedance transformer to solve this problem. For this purpose, the authors develop a numerical algorithm. Firstly, a model of the frequency dependent effective permittivity is selected. Secondly, the voltage, current and effective power transfer functions are shown for the tapered line. And the distortion obtained by using these functions are shown for the non ideal square pulse along the exponential taper. The authors find that the relaxation oscillation in the distorted wave is caused by the dispersion of the taper. The sustained tail and descend of gentle slope in the plateau are caused due to the multi reflection in the tapered line and are inherent characteristics in the taper line.Through this numerical algorithm, results are presented for comparison of three different tapers (exponential, triangular and Chebysheff distributions). The wave response and power conversion efficiency are two factors for comparison.The results of calculation show that, by using tapered line impedance transformer, the following aspects are improved: 1. The pulse power conversion efficiency. 2. The output optical pulse waveform.